Hydrogen sulfide (H₂S), a novel gas signaling molecule, has been shown to enhance plant resistance to various abiotic stresses. Here, we investigated the effect of sodium hydrosulfide (NaHS, a H₂S donor) on the growth, photosynthetic parameters, and enzyme activities related to carbon and nitrogen metabolism, as well as the levels of carbohydrates and nitrogen metabolites in foxtail millet seedlings subjected to drought stress conditions in pots. The findings revealed that drought stress led to a significant 41.2% decline in the total dry weight (DW) after 12 days of treatment, whereas plants treated with NaHS showed a lesser reduction of 18.7% in total DW. Under drought stress, exogenous NaHS was found to enhance carbon metabolism in foxtail millet seedlings by significantly enhancing photosynthetic capacity, starch, and sucrose content. Additionally, exogenous NaHS was observed to improve nitrogen metabolism by substantially increasing soluble protein content, nitrogen assimilate activity, and synthesis of nitrogen-containing compounds in foxtail millet seedlings. In summary, the exogenous application of NaHS stimulated seedling growth and enhanced drought resistance in foxtail millet by modulating carbon and nitrogen metabolism processes affected by drought stress.

Both melatonin and hydrogen sulfide (H₂S) mitigate chromium (Cr) toxicity in plants, but the specific interaction between melatonin and H₂S in Cr detoxification remains unclear. In this study, the interaction between melatonin and H₂S in Cr detoxification was elucidated by measuring cell wall polysaccharide metabolism and antioxidant enzyme activity in maize. The findings revealed that exposure to Cr stress (100 μM K₂Cr₂O₇) resulted in the upregulation of L-/D-cysteine desulfhydrase (LCD/DCD) gene expression, leading to a 77.8% and 27.3% increase in endogenous H₂S levels in maize leaves and roots, respectively. Similarly, the endogenous melatonin system is activated in response to Cr stress. We found that melatonin had a significant impact on the relative expression of LCD/DCD, leading to a 103.3% and 116.7% increase in endogenous H₂S levels in maize leaves and roots, respectively. In contrast, NaHS had minimal effects on the relative mRNA expression of serotonin-Nacetyltransferase (SNAT) and endogenous melatonin levels. The production of H₂S induced by melatonin is accompanied by an increase in Cr tolerance, as evidenced by elevated gene expression, elevated cell wall polysaccharide content, increased pectin methylesterase activity, and improved antioxidant enzyme activity. The scavenging of H₂S decreases the melatonin-induced Cr tolerance, while the inhibitor of melatonin synthesis, p-chlorophenylalanine (p-CPA), has minimal impact on H₂S-induced Cr tolerance. In conclusion, our findings suggest that H₂S serves as a downstream signaling molecule involved in melatonin-induced Cr tolerance in maize.

Membrane lipid remodeling represents a crucial adaptive mechanism for plants in response to drought stress. This study investigated the regulatory influence of melatonin on the photosynthetic attributes, oxidative damage, and lipid metabolism of foxtail millet seedlings subjected to drought stress, with particular emphasis on alterations in lipid composition and fatty acid unsaturation. The findings indicated that melatonin treatment markedly enhanced the drought tolerance of foxtail millet seedlings, resulting in increases in chlorophyll content, net photosynthetic rate, and total dry weight by 51.2%, 39.8%, and 51.1%, respectively. Melatonin increased the levels of monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG), and phosphatidylcholine (PC), while promoting the accumulation of unsaturated fatty acid (18:3) and leading to an increase in the double bond index (DBI). Concurrently, there were significant alterations in the expression of genes associated with glycolipid and phospholipid biosynthesis, aligning with the observed changes in lipid components. These findings indicate that melatonin potentially enhances the drought tolerance of foxtail millet seedlings through the regulation of lipid metabolic reprogramming. This process involves an increase in the content of unsaturated fatty acids and an optimization of the lipid unsaturation index, which collectively contribute to the greater stability, fluidity, and integrity of cellular membranes.